Oil shale is a natural sedimentary rock containing an abundance of residual organic material which, when processed, can be made into oil and fuel products. Typically, oil shale, such as exemplified by the Green River formation in Wyoming, Colorado and Utah, has about 15-20% organic material embedded in an inorganic mineral matrix. The organic portion is composed generally of a soluble bitumen fraction and an insoluble fraction in which kerogen constitutes the bulk of the insoluble organic material. In order to remove the organic material from the oil shale, the usual process has comprised crushing the matrix rock and subjecting the crushed matrix to heat in a retort to distill off the kerogen by destructive pyrolysis. A major waste product from oil shale retorting processes is water coproduced with the shale oil and which can also include a small amount of water originally trapped within the matrix of the oil shale. The amount of retort water formed may equal 20 to 100 barrels per 100 barrels of shale oil produced. Of course, the actual amount of retort water produced depends upon the type and operating conditions of the retorting process used as well as the location and nature of the oil shale. Since the oil shale retort water is loaded with considerable quantities of soluble organic and inorganic materials, it presents a serious major disposal problem. On the other hand, the presence of organic components, particularly nitrogenous components, presents an opportunity for recovery of economic values from the retort water which can aid in making oil shale processing operations economically feasible. Such economic feasibility is often called in question when one compares the cost of deriving useful oil products from oil shale. Accordingly, any basis for recovering of economic values constitutes a significant advantage.
A number of processes have been suggested for the treatment of retort water including chemical precipitation, solvent extraction, ion exchange and limestone neutralization. Except for special circumstances there are practical limitations in the applications of all the foregoing methods. Moreover, such methods generally require continued addition of treatment chemicals which increases the quantity of contaminants, complicates the problem of ultimate disposal and decreases the opportunity for economic recoveries.
The present invention provides a process for the recovery of economic values from shale oil retort water which does not suffer the drawbacks of the above-mentioned procedures, but usefully permits recovery of ammonia. Specifically, the shale oil retort water is delivered to an electrolytic cell and a direct current potential is applied across the anode and cathode chambers of the cell at a current density sufficient to effect a substantial decrease in the organic compounds in the retort water in the anode chamber and to evolve a substantial amount of ammonia from the retort water in the cathode chamber. The ammonia can be recovered as a valuable product of the process and can be combined with carbon dioxide evolved from the anode chamber, as a result of the oxidative electrolysis therein, to provide an economic bases for the synthesis of urea or other valuable products.